1. Technical Field
The present invention relates to electronic devices and to control methods for the electronic devices, and more particularly, relates to an electronic device and to a control method for the electronic device in which, a secondary battery can be charged during reception of communication signals by using part of a signal-reception path as a charging path for supplying charging current to the secondary battery.
2. Background Art
Recently, devices which have a construction in which a small portable electronic device such as a portable terminal or an electronic watch, is placed into a charger called a xe2x80x9cstationxe2x80x9d whereby the electronic device is charged, are known.
In such a construction, a lithium-ion secondary battery, provided as a storage device for storing charged electrical energy, is provided in the small portable electronic device.
This lithium-ion secondary battery has features such as high voltage, high energy density, and relatively lower self-discharge. It is often used in small portable electronic devices (such as portable telephones, camera-integrated type videotape recorders, and notebook type personal computers) which require particularly high energy density.
When more than a so-called xe2x80x9ctolerance voltagexe2x80x9d (i.e limit voltage or maximum voltage) is applied to the above-described lithium-ion secondary battery, dendritic deposits form and then internal short-circuiting phenomena occur, which ultimately shortens the life of the battery.
Hence, in a conventional charging method, constant charging current is applied to the lithium-ion secondary battery until the charged voltage across the lithium-ion secondary battery reaches the tolerance, i.e. maximum, voltage. After the charged voltage reaches the tolerance voltage, charging is performed at a constant voltage (see Japanese Unexamined Patent Publication No. 5-111184 for details).
Moreover, when charging is performed between a small portable electronic device and the charger, a limiter circuit for limiting the increase in voltage across the battery is provided so that the battery voltage across the lithium-ion secondary battery does not exceed the tolerance voltage.
Not only charging, but also communication, is performed between the small portable electronic device and the charger by using of a charging path and a signal-receiving path. In addition, in a case in which charging and data communication are performed using the same system (for example, an electromagnetic coupling system or an optical coupling system) the battery voltage across the lithium-ion secondary battery must be controlled so as not to exceed the tolerance voltage by causing the above-described limiter circuit to operate so that the battery voltage across the lithium-ion secondary battery does not exceed the tolerance voltage while charging is performed.
However, when a small portable electronic device receives a signal and the limiter circuit is activated, the limiter circuit prevents voltage variations from being conducted to a reception circuit. Accordingly, the reception circuit fails to receive the signal.
Therefore, the limiter circuit is constructed so as to be inactive while communication is performed.
Accordingly, when a small portable electronic device receives data, there is an advantage in that the small portable electronic device can be charged using surplus electric power not required for communication. However, when the battery voltage across the lithium-ion secondary battery of the small portable electronic device is close to the tolerance voltage, there is a problem in that the battery voltage across the lithium-ion secondary battery may exceed the tolerance voltage since the limiter circuit is deactivated during data reception, which shortens the life of the lithium-ion secondary battery.
Accordingly, objects of the present invention are to provide an electronic device and a control method for the electronic device in which the voltage across the secondary battery can be prevented from exceeding its tolerance voltage (i.e. its maximum rated voltage) and the secondary battery can be prevented from being degraded when receiving-time charging current during periods of data communication.
An electronic device according to the present invention is characterized in that there is provided a storage device on which charging can be performed from the outside, and the charged voltage of the storage device is controlled so as not to exceed a predetermined tolerance, or maximum, voltage. The electronic device further includes a reception device for receiving a signal from the outside, and a charging-current-control means for controlling a charging currentapplied to the storage device resulting from the signal reception, so that the voltage across the storage device does not to exceed the tolerance voltage. By using part of a signal path to the reception device as a charging path to the storage device, the storage device may be charged at the time that the reception device receives signals.
An electronic device according to another aspect of the present invention includes a storage device in which charging can be performed from the outside, and the charged voltage of the storage device is controlled so as not to exceed a predetermined tolerance voltage. The electronic device further includes a reception circuit to receive a signal from the outside, whereby the application of a charging current to the storage device is enabled at the time of signal reception by using part of the signal-reception path to the reception circuit as a charging current path to the storage device. The electronic device is characterized in that there is provided an energy balance control means for controlling the accumulated voltage across the storage device so as not to exceed its tolerance voltage by controlling a balance between charge energy to the storage device and discharge energy from the storage device.
An electronic device according to still another aspect of the present invention includes a storage device in which charging can be performed from the outside of the electronic device, and the charge voltage is controlled so as not to exceed a predetermined maximum voltage. and the electronic device further includes a reception circuit to receive a signal from the outside, wherein reception of a signal by the reception device causes charging of the storage device by using part of a signal path to the reception device as a part of a charging path to the storage device. The electronic device is further characterized by a charging-current-control means and a switching means. The charging-current-control means is provided with an accumulated voltage detection means for measuring the accumulated voltage across the storage device. The switching means is provided between the reception device and the storage device and is effective for causing the reception device and the storage device to be disconnected when the accumulated voltage detected by the accumulated voltage detection means exceeds the maximum voltage.
A control method is provided for an electronic device according to the present invention, which includes a storage device that can be charged from the outside and whose charge voltage is controlled so as not to exceed a predetermined maximum voltage, and a reception circuit to receive a signal from the outside. By using part of a charging path to the storage device and as a signal path to the reception circuit, the storage device may be charged while the reception device is receiving signals. The control method for an electronic device is characterized in that there are provided a voltage measuring step for measuring the voltage across the storage device and a charging-current-bypass step for controlling the voltage across the storage device so as not to exceed the tolerance voltage, by bypassing away from the storage device, the charging currentresulting from the reception, by a predetermined amount based on the measured voltage across the storage device.